1. Field of the Invention
The present invention relates to a power management device and method thereof, especially to a power management device and method used in a multiprocessor system.
2. Description of the Related Art
Due to the well-development of computer systems, it's getting difficult to dramatically increase speed of central processing unit (CPU). Thus, the trend for research and developments turns into multiprocessor system for improvement in operation speed of computer system. The multiprocessor system is generally consisted with a plurality of CPUs, and disposed in a computer system for improving operation speed of the computer system.
Since the CPU is one of the most power-consumptive components in the computer system, a lot of power will be consumed when a plurality of CPUs of the multiprocessor system runs at the same time, and thus a power management of the multiprocessor system is concerned. Among the power management technology for the multiprocessor system available now, there is an open industry specification—Advanced Configuration and Power Interface (ACPI) for efficient power management in the computer system, and the CPU could work in four processor power states, C0 state, C1 state, C2 state, and C3 state. The C0 state is that the CPU executes instructions while the C1, C2, C3 states are low power states in different levels. Particularly, the C3 state is in a sleep mode, which is the most electricity-saving state of the CPU.
Refer to FIG. 1, a first CPU 10 and a second CPU 12 respectively couple to a north bridge (NB) chip 14 by a mutual bus in the multi-processor system. An operating system shuts down an arbiter 15 of the NB chip 14 until the CPUs 10, 12 trans it to the C0 state before, and the NB chip 14 stops sending any event from the NB chip 14 to the CPUs 10, 12 in the C3 state therefore. After the arbiter 15 is shut down, a south bridge (SB) chip 16 sends a control signal to the CPUs 10, 12 for entering the C3 state. Both of the CPUs 10, 12 can't snoop any events.
The NB chip 14 will shut down the arbiter 15 to stop transit the events when one of the CPUs 10, 12 enters the C3 state, and all of the CPUs can't snoop the events no matter the CPUs is in C3 state or not. However, if the arbiter 15 is not be shut down and sends events to the CPU not in the C3 state, the CPUs will snoop the events and the CPU not in C3 state gets problems cause of the mutual bus. Thus, the CPUs of the multiprocessor system have to enter or leave the C3 state synchronously. In other words, each CPU is forced to be out of the C3 state when any CPU is waked up from the C3 state. Therefore, the most power-saving status can't be achieved.
The present invention provides a power management device for multiprocessor system and method thereof that overcomes shortcomings mentioned above of the multiprocessor system.